Autoconvergence of a cathode ray tube using a semiconductor detector

Abstract

A CRT calibration system is provided having a CRT with a display screen, an electron gun system, and a plurality of feedback elements. Each feedback element has an active area disposed proximately to the display screen at a preselected location such that an electron beam from the electron gun system can strike at least a portion of the active area. In response to being struck by electrons, each feedback element provides a feedback signal related to the area of the portion struck. The system also includes a detector system for detecting each feedback signal, and an integrating analog-to-analog converter which, in response, provides a digital signal related to the portion of the active area struck and thereby to the position of the electron beam relative to the particular feedback element interrogated. Also included is a control system for directing the electron beam to strike a sequence of portions of the active area for each feedback element, thereby evoking a corresponding sequence of feedback signals for each feedback element and a corresponding sequence of digital signals, enabling the control system to determine the location of each feedback element.

I claim: 
     
       1. A cathode ray tube calibration system comprising: a cathode ray tube having: a display screen;   electron gun means for producing an electron beam directed toward said display screen;   feedback means having an active surface disposed proximately to said display screen at a preselected location such that said electron beam can be directed to strike at least a portion of said active surface, for providing a feedback signal which is related to the area of said portion that is struck;     detector means for detecting said feedback signal and for providing a second signal in response thereto which is a function of said area of said portion that is struck;   converter means for integrating said second signal and for issuing a digital signal in response thereto;   control means for directing said electron beam to strike a sequence of portions of said active surface thereby evoking a sequence of said feedback signals, a sequence of said second signals, and a sequence of said digital signals, and for determining a location of said feedback means based on said sequence of digital signals.   
     
     
       2. A system as in claim 1 wherein said cathode ray tube further includes a shadow mask interposed between said display screen and said electron gun means, and wherein said feedback means comprises a phosphorescent material disposed at a preselected location on a surface of said shadow mask facing said electron gun means. 
     
     
       3. A system as in claim 2 wherein said cathode ray tube has a vertical spacing of dimension V between horizontal raster lines and wherein said cathode ray tube provides pixels having a horizontal extent H wherein said feedback means is configured as two legs of a right triangle, with a first leg oriented vertically and a secong leg inclined at an acute angle α whose tangent is V/H. 
     
     
       4. A system as in claim 2 wherein said detector means comprises a photodiode operated in a photovoltaic mode. 
     
     
       5. A system as in claim 4 wherein said detector means comprises a transimpedance amplifier coupled to receive input signals from said photodiode, said transimpedance amplifier providing said second signals in response thereto. 
     
     
       6. A system as in claim 5 wherein said converter means comprises an integrator coupled to receive said second signals, and a comparator coupled to receive integrated signals from said integrator, said comparator comparing said integrated signals with a signal having a level equal in magnitude to an integrated signal from said integrator indicating a reference position of said electron beam on said feedback means, and providing said digital signals corresponding to that comparison. 
     
     
       7. A system as in claim 6 wherein said control means comprises processor means for causing said cathode ray tube to produce a sequence of raster bars, each raster bar having at least one raster line segment, and for directing each of said raster bars into one of a number of selected locations within a known distance of said feedback means. 
     
     
       8. A system as in claim 7 wherein said control means further comprises logic means coupled to receive said sequence of digital signals from said converter means for selecting said locations for each of said raster bars in response to said sequence of said digital signals. 
     
     
       9. A system as in claim 8 wherein said logic means selects one of said locations in response to each of said digital signals in said sequence of digital signals. 
     
     
       10. A system as in claim 9 wherein said logic means executes a successive approximation algorithm to select each of said locations to iteratively arrive at a location of the feedback means. 
     
     
       11. A system as in claim 10 wherein said logic means further comprises register means for storing information corresponding to said location of said feedback means and for providing a signal containing said information to said processor means. 
     
     
       12. A system as in claim 11 wherein said processor means further comprises correction means for correcting electron beam position on said display screen in response to said information regarding feedback means location. 
     
     
       13. A system as in claim 1 wherein said converter means comprises an integrator coupled to receive said second signals and a comparator coupled to receive integrated signals from said integrator, said comparator comparing said integrated signals with a fixed voltage equal in level to an integrated signal from said integrator corresponding to a preselected portion of said active surface being struck by said electron beam, and providing said digital signals corresponding to that comparison. 
     
     
       14. A system as in claim 13 wherein said control means comprises processor means for causing said cathode ray tube to produce a sequence of raster bars, each raster bar having at least one raster line segment, and for directing each of said raster bars into one of a number of selected locations within a known distance of said feedback means. 
     
     
       15. A system as in claim 14 wherein said control means further comprises logic means coupled to receive said sequence of digital signals from said converter means for selecting said locations of each of said raster bars in response to said sequence of said digital signals. 
     
     
       16. A system as in claim 15 wherein said logic means selects one of said locations in response to each of said digital signals in said sequence of digital signals. 
     
     
       17. A system as in claim 16 wherein said logic means executes a successive approximation algorithm to select each of said locations to iteratively arrive at a location of said feedback means. 
     
     
       18. A system as in claim 1 wherein said cathode ray tube comprises a plurality of said feedback means disposed at preselected locations spaced about in proximity of said display screen. 
     
     
       19. A system as in claim 7 wherein each of said raster bars comprises a plurality of parallel raster line segments. 
     
     
       20. A system as in claim 14 wherein each of said raster bars comprises a plurality of parallel raster line segments. 
     
     
       21. A cathode ray tube calibration system comprising: a cathode ray tube having: a display screen;   electron gun means for producing an electron beam directed toward said display screen;   feedback means having an active surface disposed proximately to said display screen at a preselected location such that said electron beam can be directed to strike at least a portion of said active surface, for providing a feedback signal which is related to the area of said portion that is struck;   detector means for detecting said feedback signal and for providing a second signal in response thereto which is a function of said area of said portion that is struck;   converter means for integrating said second signal and for issuing a digital signal in response thereto;   control means for directing said electron beam to surface, execute a sequence of raster line segments, each of said segments striking different portions of said active surface lying on the same raster line, thereby evoking a sequence of said feedback signals, a sequence of said second signals, and a sequence of said digital signals, and for determining a location of said feedback means based on said sequence of digital signals.     
     
     
       22. A method of measuring electron beam position in a cathode ray tube relative to a feedback element located in said cathode ray tube in a position to be struck by said electron beam, said feedback element issuing a signal functionally related to the area struck by said electron beam, comprising the steps of: (a) providing a sequence of sets of electron beam line segments, each set having a geometric extent which when said set is moved into coincidence with a portion of said feedback element for a preselected period of time will cause said feedback element to issue a feedback signal related to the position of said set relative to said feedback element;   (b) detecting said feedback signals and issuing a sequence of second signals in response to said feedback signals, each second signal in said sequence being functionally related to the area struck by each set of raster line segments;   (c) integrating each second signal over time to obtain a single value for each second signal, each single value related to the position of the corresponding set of raster line segments;   (d) selecting the sequence of sets of raster line segments to provide a measure of the position of said feedback element.   
     
     
       23. The method of claim 19 wherein the selection of step (d) is according to a successive approximation algorithm.